Method of forging metals



Patented Sept. 29, 1953 METHOD OF FORGING METALS Edward C. Creutz,Pittsburgh, Pa., assignor to the United States of America as representedby the United States Atomic Energy Commission No Drawing. ApplicationDecember 24, 1946, Serial No. 718,263

This invention relates to a method forming beryllium metal into variousintricate shapes and the unit used for carrying out the process. Theinvention is of particular utility in the formation of intricate shapesof beryllium metal and is particularly useful where the beryllium metal,so formed, is to be used as a moderator in a chain reacting neutronicreactor. It is of primary importance in such applications that theberyllium metal be of a high degree of purity. In the past, the alloyingof materials such as titanium and zirconium with beryllium metal havebeen employed in attempts to secure hot workability of the berylliummetal; but in the use of beryllium metal as a moderator in a neutronicreactor, the introduction of materials having a high neutronic dangercoefficient, such as titanium and zirconium cannot be tolerated.

It is, therefore, the purpose of this invention to provide a method offabricating beryllium metal of high purity into various intricateshapes, and also to produce fabricated shapes possessing over allhomogeneity related to the physical structure of the metal.

A more specific object of the invention is to provide a fabricatedarticle of beryllium which is uniform as to physical characteristics sothat similar physical properties, such as: thermal conductivity,coefii-cient of expansion, tensile properties and hardness, will becorrespondingly the same in successive fabricated shapes.

A further object of this invention is to provide a method of fabricatingberyllium metal by a forging process, whereby the surface of thefabricated beryllium article will be free from imperfections such asgalling, warpage and incipient cracks.

In the past, beryllium metal has been one of the very few metals thathas not become malleable despite successful attempts to raise the purityof the beryllium metal close to 100 percent. Besides raising the puritythrough refined methods of reducing the metalfrom the ore and throughdistillation of vacuum melted metals, attempts have been also made tosecure workability of the metal through controlled grain size.

In accordance with the present invention beryllium metal is encasedwithin a jacket of metal capable of being forged such as steel andcopper, wherein the beryllium metal is confined within the jacket; andthen the encased billet of beryllium metal is subjected to a forgingoperation. The beryllium metal is thus fabricat-,

ed into various shapes as is the jacket. material 6 Claims. (Cl. 78-81)I encasing the beryllium billet. At the same time operation, it wasobserved that chilled cast beryllium had no appreciable ductility eitherin compression or in tension at room temperature; because of this coldworking of the metal was not'possible. At temperatures around 800- C. orhigher the metal tends to exhibit ductility so as to be fabricated by ahot forming process. By studying the curves drawn from the comparativeresults for compressive strength versus temperature for beryllium metal,it should be noted that the strength properties may be correlated with adecrease in the proportional limit of the metal and that the rate ofdecrease becomes greater with additional temperature increments whereinthe ductility of the metal in creased markedly above 600 C. Thisbehavior may be associated with recrystallization temperature of theberyllium metal, which is about 700 C., and also with a change in the.mechanism of deformation.

The forging of beryllium was made originally on cast beryllium billetswherein the metal was heated over a varied temperature range from about500 C. to about '1200 C. and the metal cracked immediately upon lightblows of the forging hammer; and the fractures obviously followed theboundaries of the coarse radial crystals. In order to improve thestructure of the cast beryllium metal and thus to improve the physicalproperties, such as malleability and ductility, the teachings of theinvention relates to a method of fabricating the beryllium metal byencasing the billet with a forgeable material, such as iron or copper,and then-subjecting the encased billet to a forging operation.

The specific requirements of the jacket material is that the metal bereadily 'forgeable under temperature and pressureconditionsat which theberyllium metal is to be subjected. .Since the beryllium melts at atemperature of about 1264? 0:2", the maximum working temperature rangeshould not exceed the melting, point-off 3 the beryllium metal; andpreferably, the maximum working temperature of the beryllium metalencased in a jacket shall not be greater than the melting point of theminimum melting temperature of the eutectic alloy of the beryllium metaland the forgeable jacket material.

In accordance with the present invention the forgeable jacket ofmaterial should be of such material that when the encased cast berylliumbillet is subjected to upsetting so as to break up the columnar grainsof the beryllium metal, the jacket material is able to withstand themechanical forces to which the encased specimen is subjected to underforging operation, The specific advantages of the metal jacket are thatthe metal jacket will afford an enclosure so as to confine the berylliummetal within the jacket so that when the metal is subjected to a forgingoperation the beryllium metal will not break apart but will be confinedwithin the metallic jacket. The fabrication of cast beryllium billets byenclosing beryllium with a jacket of forgeable metal affords not only ashield to the beryllium metal as to so reduce the formation of oxidesduring the operation, but also will afford a lubricating interfacebetween the striking surfaces of the forging hammer and the berylliummetal proper.

In accordance with one embodiment of the present invention it was foundthat when cast beryllium billets, approximately two inches in diameterand four inches long, were enclosed in a metallic jacket, preferably ofsoft low carbon steel of SAE 1020 specifications and then subjected to aforging operation, a fabricated shape of beryllium metal may be formed.These steel jackets were approximately one-half inch thick andcompletely surrounded the beryllium billet. The encased beryllium billetwas heated to a temperature in excess of 1160" C. and then subjected toa forging operation. It was noted that by upsetting the encasedberyllium billet deformation of the metal resulted and a new shape wasattained having superior physical properties as compared with theoriginal cast beryllium billet.

The formation of an objectionable alloy layer at the interface betweenthe beryllium metal and the iron jacket was noted in the fabrication ofa beryllium shape when the metal was worked at a temperature in excessof the alloying temperature. This alloy was shown to form at about 1150C. On comparative operations and according to the alloy phase diagram, aminimum melting eutectic of iron and beryllium will have a melting pointtemperature of about 1155 C. In order to obviate this alloying conditionin the upsetting operation, a layer of an inert refractory material isinterposed between the metallic jacket and the beryllium billet bywashing the billet with the refractory material and then tamping in therequired amount. This layer is approximately of an inch thick. A layerof calcium oxide is preferred in the operation although other refractoryoxides such as beryllium oxide and thorium oxide are also satisfactory.Upon subjecting this encased billet having the oxide layer interposedbetween the metallic jacket and the beryllium metal to a forgingoperation a superior structure of beryllium metal is obtained. A casberyllium billet can be also jacketed with other materials which aremore readily forgeable than beryllium such as copper and satisfactoryresults can be obtained. An objection to the use of copper may a sencebe primarily accorded to the lower melting point of the copper-berylliumeutectic which is about 865 C. and it has been found that superiorfabricated shapes may be obtained when subjecting the beryllium billetto a forging operation in excess of 865 (3.; therefore, it is preferableto use a low carbon steel jacket.

The utilization of an inert refractory material interposed between thejacket material and the beryllium billet is primarily used as amechanical means to separate the boundary interface of the berylliummetal and the jacket material. Since it is desirable to remove thejacket material subsequent to the upsetting operation the use of theoxide layer affords a parting means whereby a relatively simpleseparation can be obtained and also it reduces the opportunity for theformation of the alloying layer between the metallic jacket and theberyllium metal.

A preferred method for upsetting cast beryllium metal is to encase theberyllium billet with a low carbon steel jacket corresponding to SAE1020 specifications and then to interpose a thick liner of calcium oxidebetween the jacket and the beryllium billet. The beryllium billet shallbe totally enclosed; and then the jacket assembly shall be completelywelded as integral unit. The encased beryllium billet is heated andsoaked to a temperature of about 1000 C. and then subjected to a forgingoperation wherein the encased beryllium billet is forged perpendicularlyto the billet axis. It was found that when upsetting the cast berylliumbillet in such a manner, superior fabricated shapes of beryllium metalare produced. It also shall be noted that when encased beryllium billetsare forged in a side-directional manner satisfactory fabricated shapesare attained. Reductions in area up to about 9b% of the original castberyllium shape can be attained in such practic and the beryllium billetexhibited physical properties which are free from surface imperfectionsand are uniform as to grain-size, tensile strength, hardness andelongation.

This procedure of encasing a metal to be forged, such as beryllium, maybe adapted to other metal materials such as thorium in which a similarforging operation has provided satisfactory fabricated shapes. Theinterposition of a refractory oxide layer such as thorium oxide betweenthe thorium and the copper jacket has yielded fabricated shapes farsuperior to those experienced in the conventional manner of forging themetal.

In general, it may be said that the processes disclosed in the presentapplication are illustrative, rather than limiting in scope, and thatall of the numerous equivalents and modifications which would naturallyoccur to those skilled in the art are included in the scope of thepresent invention. Only such limitations as are indicated in theappended claims should be imposed on the scope of this invention.

What is claimed is:

1. The method of forging beryllium metal comprising the steps of forminga unit by encasing a beryllium billet within an envelope of a metalcapable of being forged and interposing a stratum of an inert refractoryoxide between the peripheral surface of the beryllium billet and innersurface of the metallic jacket and then subjecting at least a portion ofthe unit to a forging operation within a range of temperature from about700 C. to the melting temperature of the minimum melting eutectic of theberyllium and said forgeable metal.

2. The method of forging beryllium metal comprising the steps ofencasing a beryllium billet Within an iron jacket and preventing contactbetween the beryllium billet and the iron jacket by interposing a layerof an inert refractory oxide intermediate therebetween, and thensubjecting at least a portion of the encased beryllium billet to aforging operation Within a temperature range from about 700 C. to lessthan the melting temperature of the minimum melting eutectic of theberyllium-iron alloy system.

3. The method of forging beryllium metal comprising the steps ofencasing a beryllium billet within a jacket of copper and preventingcontact between the beryllium billet and the copper jacket byinterposing a layer of calcium oxide therebetween; then subjecting atleast a portion of the encased beryllium billet to a forging operationwithin a temperature range from about 700 C. to less than the meltingtemperature of the minimum melting eutectic of the berylliumcopper alloysystem.

4. A method of forging beryllium metal comprising the steps of encasinga beryllium billet with a low carbon steel jacket, interposing a layerof calcium oxide between the steel jacket and the beryllium metal andthen subjecting at least a portion of the encased beryllium billet to aforging operation at a temperature from about 850 C. to about 1150 C.

5. The method of forging beryllium metal comprising the steps of placinga beryllium billet within a metal jacket, preventing contact between thebillet and the jacket by interposing a layer of an inert refractoryoxide, and subject- 6 ing the encased billet to a deformation operationat a temperature above 700 C. and below the melting point of beryllium,said metal jacket having a melting point above the temperature of thedeformation operation.

6. A method of forging beryllium metal comprising subjecting a compositeunit comprising a beryllium mass, a layer of an inert refractory oxidetherearound, and a metal jacket enclosing said layer to a forgingoperation within a range of temperature from about 700 C. to less thanthe melting temperature of the minimum melting eutectic of the berylliumand the metal jacket.

EDWARD C. CREUTZ.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 377,000 Withington Jan. 24, 1888 982,751 Thowless Jan. 24,,1911 2,171,439 Von Zeppelin Aug. 29, 1939 2,215,477 Pipkin Sept. 24,1940 2,257,535 Rohn et al Sept. 30, 1941 2,307,243 Slagle Jan. 5, 1943OTHER REFERENCES Schumar, AECD-l851, Uranium, Thorium and Beryllium;Melting and Fabrication, manuscript date March 23, 1948, datedeclassified April 1, 1948, 9 pages. (Copy in Patent O-fiice Library.)

Gordon, MDDC-1078, Vacuum Melting and Casting of Beryllium, manuscriptdate September, 1945, date declassified August 15, 1947, 8 pages. (Copyin Patent Ofiice Library.)

Kelly, Iron Age, volume 156, pages 68, 69, July 26, 1945. (Copy inPatent Office Library.)

1. THE METHOD OF FORGING BERYLLIUM METAL COMPRISING THE STEPS OF FORMINGA UNIT BY ENCASING A BERYLLIUM BILLET WITHIN AN ENVELOP OF A METALCAPABLE OF BEING FORGED AND INTERPOSING A STRATUM OF AN INERT REFRACTORYOXIDE BETWEEN THE PERIPHERAL SURFACE OF THE BERYLLIUM BILLET AND INNERSURFACE OF THE METALLIC JACKET AND THEN SUBJECTING AT LEAST A PORTION OFTHE UNIT TO A FORGING OPERATION WITHIN A RANGE OF TEMPERATURE FROM ABOUT700* C. TO THE MELTING TEMPERATURE OF THE MINIMUM MELTING EUTECTIC OFTHE BERYLLIUM AND SAID FORGEABLE METAL.